The present invention relates to a conductive-transmission-line waveguide converter, a microwave reception converter and a satellite-broadcast reception antenna, which are well suitable for reception of a broadcast transmitted as a cross-polarized wave modulated by broadcasted signals of a group of channels having horizontally polarized and vertically polarized waves different from each other such as a CS broadcast and an Astra satellite broadcast of Europe.
A CS broadcast and an Astra satellite broadcast of Europe are each a satellite broadcast using a cross-polarized wave modulated by signals of a group of broadcasting channels with horizontally polarized and vertically polarized waves different from each other.
Comprising a parabola-shaped reflecting mirror and a converter unit, a satellite-broadcasting reception antenna is also referred to as simply a parabola antenna. The converter unit is also referred to as a microwave reception converter. In a parabola antenna for receiving such a cross-polarized wave, the parabola-shaped reflecting mirror reflects a wave transmitted by a satellite to a converter unit. In the converter unit, the reflected wave is introduced into a waveguide by way of a horn-like portion. A polarized-wave splitter splits the wave led to the inside of the waveguide into horizontally-polarized-wave and vertically-polarized-wave components. The horizontally-polarized-wave and vertically-polarized-wave components are each subjected to frequency down conversion in a down converter for producing signals having respective frequencies predetermined for a group of channels. The signals resulting from the frequency down conversion are then supplied to a television tuner.
In the case of the satellite-broadcasting reception antenna including a polarized-wave splitter for splitting a cross-polarized wave into horizontally-polarized-wave and vertically-polarized-wave components, however, the polarized-wave splitter must be provided at a location in the middle of an electromagnetic-wave transmission route inside the waveguide. Thus, the length of the waveguide needs to be increased in the longitudinal direction. As a result, there is raised a problem of a large size. In addition, since a component dedicated to serve as a probe for taking in a horizontally polarized wave is required separately from a component dedicated to serve as a probe for taking in a vertically polarized wave, there is also raised a problem of a rising manufacturing cost.
As a conventional conductive-transmission-line waveguide converter employed in the converter unit, there has been proposed a conductive-transmission-line waveguide converter wherein a conversion unit of a microstrip line is provided inside a waveguide to separate and take in horizontally-polarized-wave and vertically-polarized-wave components from an electromagnetic wave transmitted as a cross-polarized wave.
FIG. 1 is a diagram showing a cross section of the conventional conductive-transmission-line waveguide converter. As shown in the figure, in this conductive-transmission-line waveguide converter, on one side of the longitudinal direction of a cylindrical waveguide 1, a feed horn 2 is provided. On the other side of the longitudinal direction of the cylindrical waveguide 1, a wiring board 3 is provided, being oriented in a direction perpendicular to the longitudinal direction of the waveguide 1. The wiring board 3 is typically a planar board made of a dielectric such as Teflon or the like. The wiring board 3 is provided in such a way that a portion thereof is located on a transmission path of an electromagnetic wave inside the waveguide 1. The feed horn 2 is veiled with a protection cover 4 to prevent dust or the like from entering the inside of the waveguide 1. The wiring board 3 is accommodated in a shield case 5.
Let the surface of the wiring board 3 on the side of the feed horn 2 be the front surface. In this case, on the back-surface side of the wiring board 3, an earth conductor is provided for forming a circuit implemented by a microstrip line. A probe unit 7 is created in an area on of the front surface of the wiring board 3 facing the internal space of the waveguide 1. The probe unit 7 is used for separating horizontally-polarized-wave and vertically-polarized-wave components from an eletromagnetic wave propagating inside the waveguide 1 and taking in the separated wave components.
Broadcasting-channel signals represented by the horizontally polarized and vertically polarized waves taken in by the probe unit 7 are converted into signals having respective frequencies predetermined for a group of channels by a down-converter circuit 8 created on the front-surface of the wiring board 3. The signals with the predetermined frequencies are supplied to a television tuner by way of a connector 6.
FIG. 2 is an explanatory diagram showing the probe unit 7 formed on the front surface of the wiring board 3. To put it in detail, in an area on the front surface of the wiring board 3, an earth conductor 3c is created. The area is an area in contact with the edge surface of the waveguide 1. In addition, 2 conductor lines 3a and 3b with all but equal widths are created on the wiring board 3 along axis lines Lx and Ly, which both pass through a cross point O of the wiring board 3 and the longitudinal axis of the waveguide 1, being orientated perpendicularly to each other.
Thus, an end portion of the conductor line 3a and an end portion of the conductor line 3b are placed on the wiring board 3 in the internal space of the waveguide 1. As shown in FIG. 2, the lengths of the end portion of the conductor line 3a and the end portion of the conductor line 3b on the wiring board 3 inside the waveguide 1 are slightly smaller than the inner radius of the waveguide 1. The end portion of the conductor line 3a and the end portion of the conductor line 3b on the wiring board 3 inside the waveguide 1 are used respectively as a probe P1 for taking in a horizontally polarized wave and a probe P2 for taking in a vertically polarized wave.
As shown in FIG. 2, the center line of the probe P1 on the conductor line 3a coincides with the axis line Lx and the center line of the probe P2 on the conductor line 3b coincides with the axis line Ly. The center line of the probe P1 is a line passing through the middle of each transversal line segment of the probe P1. By the same token, the center line of the probe P2 is a line passing through the middle of each transversal line segment of the probe P2. The probes P1 and P2 are laid out in such an arrangement that a horizontally polarized wave and a vertically polarized wave are taken in with a highest degree of efficiency.
In the conductive-transmission-line waveguide converter explained above by referring to FIGS. 1 and 2, 2 probes, that is, a horizontal probe and a vertical probe, can be formed on the same planar wiring board. Thus, the conductive-transmission-line waveguide converter offers a merit of a small size and a low manufacturing cost in comparison with a converter wherein a polarized-wave splitter is provided at a location in the middle of an electromagnetic-wave transmission route inside the waveguide for splitting a cross-polarized wave into horizontally polarized-wave and vertically polarized wave components.
Since the probe P1 for taking in a horizontally polarized wave and the probe P2 for taking in a vertically polarized wave are placed on the same planar wiring board, however, there is a tendency to a difficulty to obtain a good cross-polarization characteristic.
It is thus an object of the present invention addressing the problem described above to provide a conductive-transmission-line waveguide converter that has 2 probes placed on the same planar wiring board and provides good cross-polarization characteristics wherein one of the 2 probes is used for taking in a horizontally polarized wave and the other probe is used for taking in a vertically polarized wave.
In order to solve the problem described above, according to a first aspect of the present invention, there is provided a conductive-transmission-line waveguide converter including a waveguide for transmitting an electromagnetic wave, a wiring board brought into contact with a side of the waveguide opposite to a side of the waveguide for inputting an electromagnetic wave, being oriented perpendicularly to a longitudinal axis of the waveguide, a first probe provided in an area on the wiring board inside the waveguide for taking in a first linearly polarized wave, and a second probe provided in an area on the wiring board inside the waveguide for taking in a second linearly polarized wave perpendicular to the first linearly polarized wave, wherein the first probe and the second probe are created along mutually perpendicular first and second axis lines respectively, which both pass through a cross point of the wiring board and the longitudinal axis of the waveguide, and a first center line passing through the middle of each transversal line segment of the first probe is shifted from the first axis line and a second center line passing through the middle of each transversal line segment of the second probe is shifted from the second axis line in such a way that, on the wiring board, the first probe is farther separated away from the second probe.
According to a second aspect of the present invention, there is provided a microwave reception converter including a waveguide for transmitting an electromagnetic wave, a wiring board brought into contact with a side of the waveguide opposite to a side of the waveguide for inputting an electromagnetic wave, being oriented perpendicularly to a longitudinal axis of the waveguide, a first probe provided in an area on the wiring board inside the waveguide for taking in a first linearly polarized wave, a second probe provided in an area on the wiring board inside the waveguide for taking in a second linearly polarized wave perpendicular to the first linearly polarized wave, a down-converter circuit for down-converting the frequency of a signal representing the first linearly polarized wave taken in by the first probe or a signal representing the second linearly polarized wave taken in by the second probe into a predetermined frequency band, a first amplifier for amplifying a signal representing the first linearly polarized wave taken in by the first probe and executing control to turn on and off an operation to output an amplified signal obtained as a result of amplification of the signal to the down-converter circuit, and a second amplifier for amplifying a signal representing the second linearly polarized wave taken in by the second probe and executing control to turn on and off an operation to output an amplified signal obtained as a result of amplification of the signal to the down-converter circuit, wherein the first probe and the second probe are respectively created along mutually perpendicular first and second axis lines, which both pass through a cross point of the wiring board and the longitudinal axis of the waveguide, and a first center line passing through the middle of each transversal line segment of the first probe is shifted from the first axis line and a second center line passing through the middle of each transversal line segment of the second probe is shifted from the second axis line in such a way that, on the wiring board, the first probe is farther separated away from the second probe.
According to a third aspect of the present invention, there is provided a satellite-broadcasting reception antenna including a reflecting mirror for reflecting an electromagnetic wave transmitted by a satellite, and a microwave reception converter which is used for taking in the electromagnetic wave reflected by the reflecting mirror and down-converting the frequency of the electromagnetic wave into a predetermined frequency band and includes a waveguide for transmitting an electromagnetic wave, a wiring board brought into contact with a side of the waveguide opposite to a side of the waveguide for inputting an electromagnetic wave, being oriented perpendicularly to a longitudinal axis of the waveguide, a first probe provided in an area on the wiring board inside the waveguide for taking in a first linearly polarized wave, a second probe provided in an area on the wiring board inside the waveguide for taking in a second linearly polarized wave perpendicular to the first linearly polarized wave, a down-converter circuit for down-converting the frequency of a signal representing the first linearly polarized wave taken in by the first probe or a signal representing the second linearly polarized wave taken in by the second probe into a predetermined frequency band, a first amplifier for amplifying a signal representing the first linearly polarized wave taken in by the first probe and executing control to turn on and off an operation to output an amplified signal obtained as a result of amplification of the signal to the down-converter circuit, and a second amplifier for amplifying a signal representing the second linearly polarized wave taken in by the second probe and executing control to turn on and off an operation to output an amplified signal obtained as a result of amplification of the signal to the down-converter circuit, wherein the first probe and the second probe are created along mutually perpendicular first and second axis lines respectively, which both pass through a cross point of the wiring board and the longitudinal axis of the waveguide, and a first center line passing through the middle of each transversal line segment of the first probe is shifted from the first axis line and a second center line passing through the middle of each transversal line segment of the second probe is shifted from the second axis line in such a way that, on the wiring board, the first probe is farther separated away from the second probe.
In the conductive-transmission-line waveguide converter, the microwave reception converter and the satellite-broadcasting reception antenna described above, the first probe and the second probe are respectively created along mutually perpendicular first and second axis lines, which both pass through a cross point of the wiring board and the longitudinal axis of the waveguide, and a first center line passing through the middle of each transversal line segment of the first probe is shifted from the first axis line and a second center line passing through the middle of each transversal line segment of the second probe is shifted from the second axis line in such a way that, on the wiring board, the first probe is farther separated away from the second probe. Thus, the physical distance between the 2 probes each used for taking in a polarized wave increases. As a result, good cross-polarization characteristics can be obtained.
In addition, the inventor of the present invention verified that, even if the first and second center lines are separated from the first and second axis lines respectively by offsets in the configuration, the efficiencies of taking in the first and second linearly polarized waves remain almost unchanged so that, practically, the offsets raise no problem.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.